WO2005121649A2

WO2005121649A2 - Injector for liquid fuels and sequential premix burner comprising said injector

Info

Publication number: WO2005121649A2
Application number: PCT/EP2005/052563
Authority: WO
Inventors: Stefano Bernero; Christian Jörg Motz; Tom Strebel; Martin Zajadatz
Original assignee: Alstom Technology Ltd
Priority date: 2004-06-07
Filing date: 2005-06-03
Publication date: 2005-12-22
Also published as: US20070231762A1; EP1754002A2; DE102004027702A1; CN1957208A; CN1957208B; WO2005121649A3; EP1754002B1

Abstract

The invention relates to an injector (4) for liquid fuels (6a) and a premix burner, especially for combustion chambers of gas turbines, comprising such an injector (4). The injector (4) comprises a swirl nozzle (14), surrounded by a shielding air channel (11) and having an enlarged cross-section of flow in the area of a nozzle-internal swirl generator (12) for the liquid fuel (6a), which decreases towards an outlet opening of the swirl nozzle (14). The inventive injector allows operation of a premix burner at reduced admission pressure and excellent quality of atomization.

Description

Liquid fuel injector and staged pre-burner with this injector

Technical application area

The present invention relates to an injector for liquid fuel with a swirl nozzle for injecting the liquid fuel, which is surrounded by a screen air duct. The invention further relates to a staged premix burner, in particular for a combustion chamber of a gas turbine, with a swirl generator for a combustion air flow, fuel outlet openings for the gradual introduction of gaseous fuel into the combustion air flow and a central carrier which has an injector with a swirl nozzle for the injection of Has liquid fuel and an umbrella air duct.

Premix burners are often used in gas turbine plants, in which incoming combustion air is subjected to a swirl and is mixed with the fuel by injecting fuel into a premixing area. When used in gas turbines, the premix burners must cover the entire operating range with sufficient security. This operating range also includes, for example, starting up the gas turbine, in which when the burner is ignited, a fuel / air mixture must be combusted at combustion pressures and preheating temperatures close to the ambient conditions. To ensure the stability of the burner operation, the burner is in - 2 - B03 / 207-0 SF

this operating area is usually operated with a pilot stage. For reasons of symmetry, this pilot stage is arranged centrally in the burner flow field, for example in the form of a fuel lance. The fuel is added to the combustion air axially in the flow direction at the tip of the fuel lance via an injector so that there are fuel-rich zones in the flow field of the burner, thus ensuring stable operation without extinguishing the flame even at low combustion pressures and temperatures. At higher operating loads, the injection of fuel is generally reduced via the pilot stage for reducing pollutants and the burner is operated in advantageous premix mode.

Another requirement for premix burners and all other modern gas turbine burners is that the burner should be usable either for gaseous and liquid fuels. This requires a further arrangement for fuel injection, which is usually also attached to the tip of the fuel lance. To avoid gaseous backflows containing fuel in the fuel feeds to the fuel lance, the fuel injector has an annular gap on the fuel lance, from which a small amount of air flows out, based on the total burner airflow. This so-called shielding air shields the two fuel nozzles for liquid and gaseous fuel against unwanted backflows. - 3 - B03 / 207-0 SF

An example of an embodiment of such a known premix burner is shown in highly schematic form in FIG. 1 in side view (left) and top view (right). In this example, the swirl generator 1 is formed from two partial shells, which are assembled to form a cone-shaped swirl body. Air inlet slots 2 for the tangential entry of combustion air lie between the two partial shells, which are indicated in the figure by the arrows which can be seen at this point. In premix mode, this is along

Air inlet slots are introduced into the combustion air via undetectable feeders and fuel outlet openings in order to mix with the combustion air within the volume specified by the swirl generator 1. A fuel lance 3 can be seen centrally within the burner, at the end of which an injector 4 with nozzle openings for the injection of liquid fuel, gaseous fuel and for the discharge of shielding air is attached. The nozzle opening 7 for the introduction of gaseous fuel 7a can be seen in the right part of the figure in the center of the fuel lance 3. This nozzle opening 7 is surrounded by a gap 5 for the exit of shielding air 5a. The annular nozzle opening 6 in the present case for the introduction of liquid fuel βa forms the outer region of this injector 4.

In the lower load range of the gas turbine, this premix burner is operated exclusively with one of the two pilot stages, ie by injecting - 4 - B03 / 207-0 SF

liquid fuel 6a or gaseous fuel 7a via the injector 4 of the fuel lance 3. In the upper load range, in the case of gaseous fuels, it is necessary to switch completely to the premixing stage in pilot operation due to the high pollutant emissions. When burning liquid fuels in the pilot stage, an emulsion of water and oil is burned as a liquid fuel in the upper load range. By introducing the water, the flame temperature is lowered locally in the flow field. This leads to a reduction in pollutant emissions, especially nitrogen oxide emissions. In addition to pollutant emissions, combustion pulsations must also be avoided in the upper load range, which can lead to restrictions in the operating range. Particularly stable burning oil / water emulsion flames are generated with swirl injectors, also known as pressure swirl injectors. Because of the high throughput and the limited space available in the area of the tip of the fuel lance, however, such swirl injectors cause a high pressure drop on the fuel side.

Presentation of the invention

The object of the present invention is to provide an injector for liquid fuel and a premix burner with such an injector, which achieve good atomization quality with a low pre-pressure of the liquid fuel.

The object is achieved with the injector and the premix burner in accordance with patent claims 1 and 10, respectively - 5 - B03 / 207-0 SF

solved. Advantageous configurations of the injector and the front burner are the subject of the subclaims or can be found in the following description and the exemplary embodiments.

The present injector for liquid fuel comprises a swirl nozzle for injecting the liquid fuel and an umbrella air duct surrounding the swirl nozzle. In this context, liquid fuel means not only pure fuel, such as oil, but also a mixture or emulsion of this fuel with other substances, in particular an oil / water emulsion. The swirl nozzle has an internal swirl generator for the liquid fuel flowing through and widens in the area of the swirl generator to an enlarged flow cross section, which is reduced again towards the outlet opening of the swirl nozzle. The lance, which is stepped on the gas side, leaves more space for a larger nozzle than conventional injectors, which means that pressure loss can be reduced. This enables the operation of this injector with a low pre-pressure and still good atomization quality.

The swirl generator inside the nozzle is preferably designed as a swirl grille, which can extend, for example, around a central swirl body within the nozzle. Furthermore, it is advantageous to likewise arrange a swirl generator within the shield air duct surrounding the swirl nozzle. The two swirl generators can produce both swirl in the same direction and in the opposite direction. The generation of a - 6 - B03 / 207-0 SF

opposite swirl of the shielding air compared to the internal swirl generator can have a positive influence on the atomization quality of the escaping liquid fuel. The strength and direction of the twist can be used to generate one for each

Optimize the application of the optimal injection of the liquid fuel via the geometric design of the swirl generator. In one embodiment of the injector

Exit area, i.e. in particular the boundary walls of the pressure swirl nozzle and the shielding air duct at the injector outlet are designed such that the shielding air and the liquid fuel exit the injector under approximately parallel flow directions. A further embodiment provides for the shielding air to emerge from the injector at an angle of attack relative to the direction of flow of the liquid fuel, so that shear forces are exerted on the emerging liquid fuel by the shielding air. This can be achieved by suitable shaping of the outlet opening for the shielding air, in particular the outer sheath delimiting the shielding air duct. The resulting shear rate can improve the atomization result when the liquid fuel is discharged. Particularly high shear rates between the shielding air and the liquid fuel can be achieved with shielding air emerging almost perpendicular to the direction of flow of the liquid fuel.

In a further advantageous embodiment of the injector, the swirl nozzle and the one surrounding it - 7 - B03 / 207-0 SF

outer encircling, which together with the swirl nozzle forms the screen air duct, in the axial direction, i.e. arranged in the main flow direction of the liquid fuel, displaceable against each other. This enables the geometric shape of the outlet opening of the screen air to be varied by the mutual displacement. When used in a premix burner of a gas turbine combustion chamber, this shift preferably takes place as a function of the combustion air temperature and thus the load of the gas turbine. In the upper load range, the screen air speed can be reduced by a suitable shift and thus the atomization, especially the spray angle and the spray quality, can be changed.

Of course, the last-mentioned embodiments can be implemented both with and without swirl generator in the screen air duct. If a swirl generator is used in the screen air duct, the swirl angle or swirl direction can also have an additional influence on the atomization quality of the liquid fuel.

The proposed staged premix burner has such an injector at the tip of a central support for a pilot stage. This central carrier can be designed, for example, in the form of a fuel lance. The premix burner is designed so that the largest possible injector, ie an injector with the largest possible widened cross section, can be used on the nozzle-internal swirl generator. Due to the graduated fuel injection, an injection of - 8 - B03 / 207 -0 SF

gaseous fuel at the top of the carrier can be dispensed with as a pilot stage. Rather, such piloting with gaseous fuel is achieved through the staged fuel injection. For this purpose, the premix burner has at least two different groups of fuel outlet openings with separate feeds for the gradual introduction of the gaseous fuel into the combustion air flow. In one embodiment of the premix burner, one of these groups of fuel outlet openings can be formed in a part of the carrier located upstream of the injector. This group of fuel outlet openings then forms the pilot stage for gaseous fuel.

Of course, the different groups of fuel outlet openings for the staged supply of gaseous fuel can also be arranged elsewhere. This relates, for example, to an embodiment of the premix burner in which the swirl generator is formed by a plurality of partial shells which enclose a premixing chamber in the shape of a cone and between which air inlet slots are formed. All or at least part of the fuel outlet openings for the tiered

The supply of gaseous fuel is formed in the area of the air inlet openings.

Due to the special injector, the present premix burner enables operation with a reduced pressure drop on the fuel side during spray formation and, in some configurations, additionally improved spray formation. - 9 - B03 / 207-0 SF

BRIEF DESCRIPTION OF THE DRAWINGS The present injector and the premix burner with this injector are explained in more detail below on the basis of exemplary embodiments in conjunction with the drawings. Here show:

Fig. 1 schematically shows an example of a premix burner according to the prior art;

2 schematically shows an example of an embodiment of a premix burner with the present injector;

3 shows a first example of an embodiment of the injector;

4 shows a second example of an embodiment of the injector; and

Fig. 5 shows a third example of an embodiment of the injector.

Ways of Carrying Out the Invention

The structure of a premix burner according to the prior art, as shown schematically in FIG. 1, was already explained in detail in the introduction to the description. - 10 - B03 / 207-0 SF

2 now schematically shows an example of an embodiment of the present staged premix burner, in which the injector according to the invention is used. In a known manner, this premix burner has a swirl generator 1, which is composed of two partial shells which enclose a premixing chamber in the shape of a cone. Air inlet slots 2 are formed between the two partial shells, which are indicated in the right-hand part of the figure in plan view (viewing direction against the flow direction) of the premix burner. In the area of these air inlet slots 2, fuel outlet openings 10 for gaseous fuel are arranged, which are supplied with this fuel via corresponding feeds. The introduction of the gaseous fuel into the combustion air stream entering tangentially through the air inlet slots 2 results in a “mixing of the gaseous fuel with the combustion air, promoted by the swirl of the combustion air.

In the present example, a group of fuel outlet openings 10 for gaseous fuel is formed in the half of the burner near the combustion chamber, which forms one of two burner stages in the present case. A second group of fuel outlet openings 9 for gaseous fuel is arranged in the central fuel lance 3 upstream of the tip of this lance 3. This further stage for the supply of gaseous fuel can serve as a pilot stage during the start-up phase of the gas turbine, in whose combustion chamber this burner is used. Of course, the - 11 - B03 / 207-0 SF

the first-mentioned burner stage can be divided as desired into different stages which can be acted upon independently of one another with gaseous fuel. These burner stages can of course also extend over the entire axial length of the swirl generator 1.

The present injector 4 is arranged at the tip of the fuel lance 3 and can be seen in plan view in the right part of FIG. 2. The figure shows the central outlet nozzle 6 for the liquid fuel βa and the annular outlet nozzle 5 surrounding it for the shielding air 5a. The staged design of this premix burner prevents the attachment of an additional nozzle for gaseous fuel at the tip of the lance, so that more space is available for the injector for liquid fuel. This very advantageously enables the proposed injector to be used with the widened flow cross section in the region of the swirl generator inside the nozzle.

When the gas turbine is started up, a large part of the fuel is added via the fuel lance 3. Only when the load is higher is the burner operated with lower fuel proportions via the lance stage, which enable the pulsation and pollutant emission behavior to be optimized. 3 to 5 show exemplary configurations of injectors 4, as can be used in a premix burner according to FIG. 2. 3 is the geometric shape - 12 - B03 / 207-0 SF

the swirl nozzle 14 can be clearly seen. This swirl nozzle 14 is locally greatly enlarged in the flow cross section in the region of the swirl grille 12 inside the nozzle. The swirl grid is formed around a central swirl body 15. Due to the more favorable space in the tip of the lance compared to conventional injectors, a larger nozzle can be installed, which significantly reduces the pressure loss, so that this injector can be operated with reduced admission pressure and high atomization capacity. The screen air channel 11 surrounds the swirl nozzle 14. In this application example, the screen air 5a emerges from the lance tip in the axial direction. This is achieved by the geometric design of the limits of the shielding air duct 11 at the outlet end, which are parallel to the axial direction. An additional swirl grille 13 with swirl in the same or opposite direction in relation to the nozzle-internal swirl grille 12 can optionally be arranged in the screen air duct 11. The atomization quality of the liquid fuel as it emerges from the injector can be influenced by adjusting the swirl angle.

FIG. 4 shows a further example of the present injector 4, in which it is constructed similarly to that of FIG. 3. However, the injector 4 shown in FIG. 4 has different exit directions for the screen air 5a and the liquid fuel 6a. Due to the inward configuration of the outlet of the shielding air duct 11, the shielding air flow is adjusted in relation to the direction of flow of the liquid fuel βa when it exits the injector. in the - 13 - B03 / 207-0 SF

In the present example, a flow field of the screen air is forced almost perpendicular to the flow direction of the liquid fuel by the illustrated embodiment, so that a high shear rate is generated between the screen air and the liquid fuel. This high shear rate promotes the atomization effect. Here, too, a swirl grille 13 can be arranged in the screen air duct, which, particularly when generating an opposing swirl, can intensify the effect of the atomization.

Finally, FIG. 5 shows a further example of an injector 4, which is designed comparable to the injector of FIG. 4. In this example, however, the shielding air duct 11 has a variable geometry, which is achieved by the outer casing 16 being able to be moved relative to one another in relation to the swirl nozzle 14 in the axial direction. This displaceability is indicated in the figure by the double arrows. If the swirl nozzle 14 is displaced in relation to the outer casing 16, the outlet gap for the shielding air opens or closes. The shift is preferably carried out as a function of the combustion temperature and thus the load of the gas turbine. For example, in the upper load range, this injector can be used to reduce the screen air speed by increasing the screen air gap and thus changing the spray angle and spray quality.

Due to the present design of the injector or premix burner, low-pollutant and pulsation-free operation is more liquid during combustion - 14 - B03 / 207-0 SF

Fuels or fuel emulsions possible in a gas turbine combustion chamber. This is made possible above all by the combination of a gas-stage gas turbine burner on the gas side, which enables the injector, which is larger due to the local widening of the swirl nozzle, to be installed in the lance tip. The different designs of the injector can influence the atomization or spray behavior to optimize the respective applications.

15 - B03 / 207-0 SF

REFERENCE SIGN I STE

Claims

- 16 - B03 / 207-0 SF

claims

1. Injector for liquid fuel, in particular for a premix burner, with a swirl nozzle (14) for injecting the liquid fuel (6a), which is surrounded by a shielding air duct (11) for shielding air (5a) and in the area of a swirl generator (12) inside the nozzle for the Liquid fuel (6a) has an enlarged flow cross section, which reduces again to an outlet opening of the swirl nozzle (14).

2. Injector according to claim 1, characterized in that the nozzle-internal swirl generator (12) is designed as a swirl grille.

3. Injector according to claim 2, characterized in that the swirl grid extends around a central swirl body (15).

4. Injector according to one of claims 1 to 3, characterized in that an internal swirl generator (13) is arranged in the screen air duct (11).

5. Injector according to claim 4, characterized in that the channel-internal swirl generator (13) in the screen air channel (11) and the nozzle-internal - 17 - B03 / 207-0 SF

Swirl generators (12) are designed in such a way that they produce an opposite swirl.

Injector according to one of claims 1 to 5, characterized in that the injector (4) is designed such that the liquid fuel (6a) and the shielding air (5a) emerge from the injector (4) with approximately parallel flow directions.

7. Injector according to claim 6, characterized in that boundary walls of the swirl nozzle (14) and the shielding air duct (11) run approximately parallel at an outlet of the injector (4).

8. Injector according to one of claims 1 to 5, characterized in that the shield air duct (11) is formed at an outlet of the injector (4) so that the shield air (5a) exits at an angle of attack to an outlet direction of the liquid fuel (6a) to exert shear forces on the liquid fuel (6a).

9. Injector according to one of claims 1 to 8, characterized in that the swirl nozzle (14) and an outer casing (16), which in conjunction with the swirl nozzle (14) forms the screen air duct (11), in the axial direction of the injector (4th ) are arranged to be mutually displaceable. - 18 - B03 / 207-0 SF

10. Staged premix burner, in particular for a combustion chamber of a gas turbine, with a swirl generator (1) for a combustion air flow, fuel outlet openings (9, 10) with feeds for the gradual introduction of gaseous fuel into the combustion air flow and a central carrier (3), the has an injector (4) with a swirl nozzle (14) for injecting liquid fuel (6a) and a shielding air duct (11) for shielding air (5a), the swirl nozzle (14) being surrounded by the shielding air duct (11) and in the region of a swirl generator internal to the nozzle (12) for the liquid fuel (6a) has an enlarged flow cross section, which is reduced to an outlet opening of the swirl nozzle (14) again.

11. premix burner according to claim 10, characterized in that a part of the fuel outlet openings (9) for introducing gaseous fuel into the combustion air stream is formed in a part of the carrier (3) located upstream of the injector (4).

12. premix burner according to claim 10 or 11, characterized in that the swirl generator (1) is formed by several partial shells which enclose a premixing chamber in the shape of a cone and between which air inlet slots (2) are formed. - 19 - B03 / 207-0 SF

13. Premix burner according to claim 12, characterized in that at least part of the fuel outlet openings (10) for introducing gaseous fuel into the combustion air flow is arranged in the region of the air inlet slots (2) on the swirl generator (1).

14. Premix burner according to one of claims 10 to 13, characterized in that the nozzle-internal swirl generator (12) is designed as a swirl grid.

15. Premix burner according to claim 14, characterized in that the swirl grid extends around a central swirl body (15).

16. Premix burner according to one of claims 10 to 15, characterized in that an internal swirl generator (13) is arranged in the screen air duct (11).

17. premix burner according to claim 16, characterized in that the channel-internal swirl generator (13) in the shielding air duct (11) and the nozzle-internal swirl generator (12) are designed such that they produce an opposing swirl. - 20 - B03 / 207-0 SF

18. premix burner according to one of claims 10 to 17, characterized in that the injector (14) is designed such that the liquid fuel (6a) and the shielding air (5a) with approximately parallel flow directions in the axial direction of the carrier (3) from the Exit injector (4).

19. premix burner according to claim 18, characterized in that boundary walls of the swirl nozzle (14) and the screen air duct (11) at an outlet of the injector (4) extend approximately coaxially.

20. premix burner according to one of claims 10 to 17, characterized in that the shield air duct (11) is formed at an outlet of the injector (4) so that the shield air (5a) exits at an angle of attack to an outlet direction of the liquid fuel (6a) to exert shear forces on the liquid fuel (6a).

21. Premix burner according to one of claims 10 to 20, characterized in that the swirl nozzle (14) and an outer casing (16), which in conjunction with the swirl nozzle (14) forms the screen air duct (11), in the axial direction of the carrier (3 ) are arranged to be mutually displaceable.